The present invention relates in general to optical devices such as optical circulators and optical isolators, and more particularly to optical devices that can be configured as an optical circulator having three, four or any number of optical ports, or as an optical isolator having two optical ports.
As generally known, in an optical isolator, a signal in the forward direction is passed from a first optical port to a second optical port. An optical circulator is a non-reciprocal optical device which allows the passage of light from a first optical port to a second one (as in an optical isolator), while a reverse signal into the second port is totally transmitted to a third port and so on for the remaining port(s) for a so-called circulating operation. Any two consecutive ports of an optical circulator are, in effect, an optical isolator since signals travel only one way.
Optical circulator devices play key roles in fiber optical networking systems and devices, for example, in fiberoptic amplifiers, dense wavelength division multiplexing (DWDM) systems and components and optical add-drop module (OADM) components. Several types of optical circulators have been developed. Examples of current optical circulator devices include those disclosed in U.S. Pat. Nos. 5,204,771; 5,471,340; 5,872,878; 6,002,512; 6,064,522 and 6,052,228. However, manufacturing such conventional circulator devices typically requires precise alignment of each optical element, leading to a low yield and high production costs. Furthermore, such conventional circulator devices tend to be bulky and expensive.
It is, therefore, desirable to provide a compact circulator array that is cost-effective and easily manufactured, and which is capable of routing any number of input signals within one integrated circulating module. It is also desirable that an optical circulator module have optimum performance, i.e., very high isolation, very low polarization dependent loss (PDL), very low polarization mode dispersion (PMD), low insertion loss, very low cross-talk, and high power handling capability. An optical circulator should also be designed for mass production with simple assembly processes.
The present invention avoids many of the problems above and substantially achieves an optical circulator or isolator which has a very high performance and which is easily manufactured. The present invention presents optical devices which are useful for long distance and high data rate communication systems.